Cold Start Emission Reduction Monitoring System and Method

ABSTRACT

An engine emissions diagnostic is disclosed that utilizes parameters correlating to catalyst temperature to identify when an indication of degraded performance may be generated.

BACKGROUND AND SUMMARY

Vehicles may be required to meet certain emission thresholds. As such,some vehicles may use emission control devices, such as catalyticconverters, to reduce engine emissions. These devices may providevarious levels of emission reduction depending on exhaust temperature.As such, engine operation may be adjusted during an engine start toincrease temperature of the device to thereby reduce emissions byachieving earlier catalyst light-off, for example.

However, the various factors can affect performance of the aboveadjustments to increase catalyst temperature. For example, degradationof components may result in less airflow than desired, for example,which may reduce exhaust gas heat. Further, engine speed controloperation may result in adjustment of spark timing to such a degree thatspark retard is sufficiently reduced or eliminated thus resulting inreduced exhaust gas temperature and delayed catalyst light-off.

As such, in one example, the above conditions causing reduced catalystlight-off performance via reduced catalyst temperature may be detectedand utilized to indicate that vehicle emission control performance hasdegraded.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic engine diagram;

FIG. 2 shows an example cold start emissions reduction monitoringroutine; and

FIG. 3 shows an example graph plotting the catalyst delta ratio againstthe engine coolant temperature at start.

DETAILED DESCRIPTION

Internal combustion engine 10 comprising a plurality of cylinders, onecylinder of which is shown in FIG. 1, is controlled by electronic enginecontroller 12. Engine 10 includes combustion chamber 30 and cylinderwalls 32 with piston 36 positioned therein and connected to crankshaft13. Combustion chamber 30 communicates with intake manifold 44 andexhaust manifold 48 via respective intake valve 52 and exhaust valve 54.Exhaust gas oxygen sensor 16 is coupled to exhaust manifold 48 of engine10 upstream of catalytic converter 20.

Intake manifold 44 communicates with throttle body 64 via throttle plate66. Throttle plate 66 is controlled by electric motor 67, which receivesa signal from ETC driver 69. ETC driver 69 receives control signal (DC)from controller 12. Intake manifold 44 is also shown having fuelinjector 68 coupled thereto for delivering fuel in proportion to thepulse width of signal (fpw) from controller 12. Fuel is delivered tofuel injector 68 by a conventional fuel system (not shown) including afuel tank, fuel pump, and fuel rail (not shown).

Engine 10 further includes conventional distributorless ignition system88 to provide ignition spark to combustion chamber 30 via spark plug 92in response to controller 12. In the embodiment described herein,controller 12 is a conventional microcomputer including: microprocessorunit 102, input/output ports 104, electronic memory chip 106, which isan electronically programmable memory in this particular example, randomaccess memory 108, and a conventional data bus. The controller mayfurther include a keep alive memory (not shown) for storing adaptiveparameters.

Controller 12 receives various signals from sensors coupled to engine10, in addition to those signals previously discussed, including:measurements of inducted mass air flow (MAF) from mass air flow sensor110 coupled to throttle body 64; engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling jacket 114; a measurement ofthrottle position (TP) from throttle position sensor 117 coupled tothrottle plate 66; a measurement of turbine speed (Wt) from turbinespeed sensor 119, where turbine speed measures the speed of a torqueconverter output shaft, and a profile ignition pickup signal (PIP) fromHall effect sensor 118 coupled to crankshaft 13 indicating an enginespeed (N). Alternatively, turbine speed may be determined from vehiclespeed and gear ratio.

Controller 12 may include various control routines, such as cold startrapid catalyst heating routines that adjust various engine and/orvehicle operating parameters to more rapidly raise exhaust gastemperature. For example, ignition timing of one or more cylinders maybe retarded from peak torque timing during cold starting operating toincrease exhaust gas heat generation. Further, engine idle speed may betemporarily elevated after a cold start to further increase exhaust gasheat generation. Still other actions may be taken, such as air-fuelratio adjustments, valve timing adjustments, fuel injection timingadjustments, and the like. In one particular embodiment, engine idlespeed, spark timing, and engine airflow, may be adjusted during a coldstart to increase exhaust gas temperature. In another embodiment, intakevalve advance and/or retard may be used, along with spark retard andfuel injection timing and amount variations. For example, the controllermay adjust a variable valve timing system to increase positive valveoverlap (e.g., via an intake only variable valve timing unit) of atleast one cylinder during a cold start, and then adjust a fuel injectionamount and/or timing and/or spark timing.

However, other control routines may be present which may limit or varythe above exhaust heat generation adjustments. For example, detection oflow fuel quality, such as hesitation fuel, may reduce or eliminate sparkretard (in order to maintain combustion and minimum engine speed). Asanother example, flow blockages or plugs, may limit airflow increases.As still another example, variable valve unit degradation may limit oraffect valve timing adjustments or positive overlap generation. As such,diagnostic routines may be used to detect such system overrides and thecorresponding effects on exhaust gas temperature and/or catalyst lightoff during at least the first 15 seconds of vehicle operation from acold start under selected conditions, such as standard air temperaturesnear 70 degrees F. and barometric pressure near sea level.

Continuing with FIG. 1, accelerator pedal 130 is shown communicatingwith the driver's foot 132. Accelerator pedal position (PP) is measuredby pedal position sensor 134 and sent to controller 12.

In an alternative embodiment, where an electronically controlledthrottle is not used, an air bypass valve (not shown) can be installedto allow a controlled amount of air to bypass throttle plate 62. In thisalternative embodiment, the air bypass valve (not shown) receives acontrol signal (not shown) from controller 12. In another alternativeembodiment, where a mass air flow sensor is not used, inducted mass airflow may be determined using a variety of computational methods.

In an exemplary embodiment, electronic engine controller 12 may furtherinclude an on-board diagnostic (OBD) system (not shown). The OBD systemmay detect operating component degradation through various diagnosticroutines. In some instances, if a routine detects degradation, theroutine may set a diagnostic trouble code (alternatively referred to asa service code) in the electronic engine controller. Many routineswithin the on-board diagnostics system may detect emission relateddegradations in a range of operating condition of the engine.

One embodiment advantageously implements a routine to monitorhydrocarbon emissions during various operating conditions, such asduring engine cold start conditions. Such a monitoring routine maydetect, whether various cold start emissions reduction (CSER) enginecontrol strategies are effective in heating a catalyst to a desiredlight-off temperature and reducing hydrocarbon emissions. Specifically,the routine may determine if particular ignition spark retard and/orelevated idle speed strategies are effectively reducing cold startemissions. However, it should be appreciated that in some embodimentsthe routine may demonstrate the effectiveness of other CSER controlstrategies as well.

Referring to FIG. 2, an exemplary cold start emissions reduction (CSER)monitoring routine is shown. Specifically, routine 200 monitors catalysttemperature via a catalyst temperature warm-up index calculation.Furthermore the monitoring system may make a degradation determinationregarding CSER related components based on whether actual emissionsexceed a predetermined threshold when compared to reference emissionsstandards. The determined degradation may result in setting a CSERservice code in the electronic engine controller. Additionally, in someembodiments the degradation determination may result in a change inoperating parameter.

Referring back to FIG. 2, the routine begins at 210 where it isdetermined if the engine is in a start condition. In one embodiment, theCSER monitor routine may be configured to monitor emissions conditionsfor fifteen seconds following the start of the engine. Thus, thedetermination made at 210 may judge whether or not fifteen seconds haveelapsed since the start of the engine. In some embodiments, the CSERmonitor routine may further be limited to running only when the engineis started and the transmission is in a neutral position. As such, theengine may be judged to be in a start condition only when thetransmission is in neutral and less than fifteen seconds have elapsedsince the start of the engine.

It should be appreciated that in some embodiment, the CSER monitorroutine may run for a desired longer or shorter amount of time, and/ormay run during driving conditions as well.

Continuing with 210, if it is determined that the engine is not in astart condition, the routine ends, otherwise the routine moves to 220.In the illustrated embodiment, the routine may be configured to makediagnostic calculations at predetermined intervals during the CSERmonitoring time period, for example, a calculation cycle may be carriedout every one hundred milliseconds. In some embodiments, the diagnosticinterval may be adjusted to desired longer or shorter lengths based on adesired diagnostic resolution.

Continuing with 220, if it is determined that the predetermined amountof time has not elapsed, the routine loops until it is determined thatthe predetermined amount of time has elapsed. Once the predeterminedamount of time has elapsed the routine moves to 230.

At 230, the routine may calculate a reference catalyst temperatureestimate (ext_cmd_wavg_ref). The reference catalyst temperature estimatemay represent the temperature of the catalyst based on performance as ifthere are no hardware problems or unintended software algorithms. Inother words, the reference catalyst temperature estimate may representthe temperature of the catalyst during fully functioning conditions. Thereference catalyst temperature estimate may be calculated from severaloperating parameters including, a desired idle rpm (dsdrpm) which may beincreased during CSER conditions to heat the catalyst; an estimatedairflow (am_ref) based on the above desired engine speed (dsdrpm(am_ref)); and the spark timing (spk_lold_cld). In some embodiments theairflow estimation may be made based on a subset of an idle speedcontrol open loop airflow calculation. Further, the referencetemperature may be a required temperature needed to achieve a givenemissions level for the current engine starting conditions, which mayinclude engine coolant temperature, barometric pressure, airtemperature, or combinations thereof. As such, the reference temperaturemay be a function of these and other parameters.

Once the reference catalyst temperature estimate has been calculated theroutine moves to 240, where the current catalyst temperature estimate(ext_cmd_wavg) may be calculated. The current catalyst temperatureestimate may be calculated from several measured or estimated operatingparameters including, engine speed (N); spark estimate (saftot); and theobserved airmeter estimate (load). In some embodiments, the currentcatalyst temperature estimate calculation may represent the actualtemperature of the catalyst during a start condition of the engine.

It should be appreciated that the above described input operatingparameters are purely exemplary, and in some embodiments other operatingparameters may be utilized as inputs for measurements, derivations, andcalculations of the exemplary routine.

Next at 250, the delta reference catalyst temperature estimate(Delta_Ref) may be made based on the change in reference temperatureestimation from the beginning of a calculation cycle to the end of acalculation cycle. The delta reference catalyst temperature estimate mayindicate the expected catalyst temperature change according to CSERcontrol strategies. Specifically, the delta reference catalysttemperature estimate (Delta_Ref) may be calculated by subtracting thereference catalyst temperature estimate (ext_cmd_wavg_ref(beg))calculated at the beginning of the calculation cycle from the referencecatalyst temperature estimate (ext_cmd_wavg_ref(end)) calculated at theend of the calculation cycle.

Next at 260, the delta current catalyst temperature estimate (Delta_CMD)may be made based on the change in actual temperature estimation fromthe beginning of a calculation cycle to the end of a calculation cycle.The delta current catalyst temperature estimate may indicate the actualcatalyst temperature change according to CSER control strategies.Specifically, the delta current catalyst temperature estimate(Delta_CMD) may be calculated by subtracting the current catalysttemperature estimate (ext_cmd_wavg_ref(beg)) calculated at the beginningof the calculation cycle from the current catalyst temperature estimate(ext_cmd_wavg_ref(end)) calculated at the end of the calculation cycle.

Now referring to 270, the temperature warm-up index calculation may bemade. A catalyst delta ratio (CDR) may be calculated by subtracting thedelta current catalyst temperature estimate (Delta_CMD) from the deltareference catalyst temperature estimate (Delta_Ref). The difference oftwo estimates may be further divided by the delta reference catalysttemperature estimate (Delta_Ref) to produce the catalyst delta ratio. Insome embodiment, the routine may include a normalization step which maycreate a catalyst delta ratio ranging from zero to one. Moreover, thenormalized catalyst delta ratio calculation may indicate the percent ofheating loss in the catalyst between the reference estimate and theactual estimate. For example, a catalyst delta ratio of ‘0.5’ mayindicate that the catalytic temperature may have achieved only 50% ofexpected temperature value.

Continuing to 280, the calculated catalyst delta ratio can be comparedto a predetermined threshold value. In the illustrated embodiment, thethreshold value may correspond to one and a half times the expectedemission value. Further, the degradation threshold may be determinedbased on a function of the engine coolant temperature at start. Thus, byplotting the catalyst delta ratio against the engine coolant temperatureat start, it can be determined whether the catalyst delta ratio is abovethe threshold. If it is determined that the catalyst delta ratio isbelow the threshold value the routine loops back to the beginning of theroutine for another cycle of calculations. If it is determined that thecatalyst delta ratio is above the threshold, the routine moves to 290.

At 290, a service code may be set in the electronic engine controller.In some embodiments, the service code may be related to CSER, forexample, the code may state “cold start engine exhaust temperature outof range”. Furthermore, in some embodiments, setting the service codemay result in a “check engine” light to illuminate and/or otherdiagnostic routines to be initiated. Once the service code has been setthe routine ends.

The routine shown in FIG. 2 is just one example of a cold start emissionreduction engine monitoring strategy. In some embodiments the routinemay include more or less diagnostic modes than shown in FIG. 2.

It should also be appreciated that the example control/diagnosticroutines described herein are dependant upon the configuration of thevehicle control system. Note that the example control and estimationroutines included herein can be used with various engine and/or vehiclepropulsion system configurations. The specific routines described hereinmay represent one or more of any number of processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various steps, acts, or functions illustrated may beperformed in the sequence illustrated, in parallel, or in some casesomitted. Likewise, the order of processing is not necessarily requiredto achieve the features and advantages of the example embodimentsdescribed herein, but is provided for ease of illustration anddescription. One or more of the illustrated steps, acts, or functionsmay be repeatedly performed depending on the particular strategy beingused. Further, the described steps may graphically represent code to beprogrammed into the computer readable storage medium in controller 12.

FIG. 3 shows an exemplary graph of catalyst delta ratio calculationsplotted against the engine coolant temperature at start during a coldstart condition according to the above described monitoring routine. Theexample graph show results compiled over multiple tests. As shown, theplots determined by the monitoring routine to be above the threshold,are plotted as circles and may be judged to be degradations.Furthermore, the plots determined by the monitoring routine to be belowthe threshold, are plotted as squares and may be judged to fall withinacceptable operating conditions.

The results illustrated in the example graph demonstrate the accurateand robust nature of the monitoring routine. For example, theappropriation of the threshold value within the routine may allow forclear determinations of whether or not a CSER engine strategy may befunctioning effectively. It should be noted that in embodiments whereengines are equipped with electronic throttle control, degradationdeterminations may occur less frequently because the electronicallycontrolled throttle may have a large dynamic range of operation,resulting in more airflow and faster catalyst temperature increase.

Further, it will be appreciated that the configurations and routinesdisclosed herein are exemplary in nature, and that these specificembodiments are not to be considered in a limiting sense, becausenumerous variations are possible. For example, the above technology canbe applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various systems andconfigurations, and other features, functions, and/or propertiesdisclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A method for controlling a vehicle having an engine, the enginehaving an exhaust with an emission control device, comprising: during anengine start, at least temporarily adjusting an operating parameter ofthe engine to increase exhaust mass flow or temperature when needed tomore rapidly heat the emission control device; estimating temperature ofthe emission control device during said engine start; and comparing saidestimated temperature to a reference catalyst temperature required toachieve an emission threshold.
 2. The method of claim 1 wherein saidreference catalyst temperature is based on a desired engine idle speed.3. The method of claim 2 wherein said reference catalyst temperature isfurther based on an estimated airflow based on the desired engine speed.4. The method of claim 3 wherein said reference catalyst temperature isbased on an expected spark value for current conditions.
 5. The methodof claim 4 wherein actual spark timing is adjusted based on fuelquality.
 6. The method of claim 1 wherein said emission threshold isbased on engine coolant temperature at start.
 7. A method forcontrolling a vehicle having an engine, the engine having an exhaustwith an emission control device, comprising: during an engine start, atleast temporarily adjusting at least engine airflow and spark timing toincrease exhaust mass flow and temperature when needed to more rapidlyheat the emission control device; overriding at least one of said engineairflow and spark timing adjustments to compensate for an operatingcondition; and setting a diagnostic indication when said override hascaused temperature of the emission control device to be lower thandesired to meet an emission level.
 8. A method for controlling a vehiclehaving an engine, the engine having an exhaust with an emission controldevice, comprising: during an engine cold start, at least temporarilyadjusting at least engine airflow and spark timing to increase exhaustmass flow and temperature when needed to more rapidly heat the emissioncontrol device; overriding at least one of said engine airflow and sparktiming adjustments to compensate for fuel quality effects on combustion;and setting a diagnostic indication when said override has causedtemperature of the emission control device to be lower than desired tomeet an emission level.
 9. The method of claim 8 wherein said overridecompensates for hesitation fuel.
 10. The method of claim 8 wherein saidoverride compensates for engine speed falling below a selected enginespeed profile during said start.
 11. The method of claim 8 wherein saiddiagnostic indication sets a code in a controller of the vehicle. 12.The method of claim 8 wherein said emission level is based on enginecoolant temperature at start.